Magneto-optical recording media are typically constructed of a magneto-optical recording layer provided on a transparent substrate of, for example, glass or plastic. The recording layer is typically made of a metal material, and can record data either optically (by recording phase changes) or magnetically (by recording direction of magnetization).
To magnetically record data onto the recording layer, a laser beam is projected on a portion of the recording layer, the laser heats that portion of the recording layer, increasing its temperature to above the material's Curie temperature, or to a point above the vicinity of the magnetic compensation temperature. At this temperature, the magnetic coercive force (Hc) of this portion of the recording layer becomes zero or substantially zero. An external magnetic field (bias magnetic field) is then applied to the heated portion of the recording layer. When the laser beam energy is removed, the temperature of the portion of the magnetic recording medium is reduced, and the magnetization is recorded. This type of recording is referred to as thermomagnetic recording.
To record the direction of the external magnetic field at high speeds, it is desirable to make the magnetic head (i.e., a coil and coil core) of the external magnetic field generating device as small as possible. However, this results in a smaller magnetic field. In order to compensate for the reduced size of the magnetic recording field, the distance between the magnetic head and the magnetic recording medium must also be reduced. For some applications, the distance between the magnetic head and the magnetic recording medium is in the range of microns. As an example, in applications capable of direct over-write recording (re-recording without first erasing previously recorded data), the gap between the magnetic head and the disk can be as small as a few microns (.mu.m).
With such small gaps between the magnetic recording head and the magneto-optical disk, there is a danger of the recording head contacting or "crashing" onto the disk during operation, while the disk is being rotated at high speed, resulting in injury to the head or loss of data from the disk.
In order to minimize any potential damage caused by the magnetic head crashing into the magneto-optic disk, magneto-optic recording media may optionally comprise a coating that acts as a lubricating layer. The lubricating layer has a relatively low coefficient of friction. Therefore, when contact occurs between a disk and a magnetic head, even at very high speeds, the lubricating layer prevents damage of the head or disk by allowing the head to slip away from the disk.
Past coatings have used silicone compounds as lubricating agents. However silicone compounds, and especially polydimethylsiloxanes, can tend to be incompatible with the radiation-curable components of coating solutions. Polydimethylsiloxane compounds that are mixed with these radiation-curable components may result in coated surfaces having cosmetic defects such as hazing, an orange peel texture, or other cosmetic imperfections.